Instead of powder, use a premixed joint compound to fill drywall seams.
Take plenty of time to fill the recess between the tapered edges of drywall with joint compound.
Apply a second coat of joint compound after the first has dried thoroughly.
Apply a third layer of joint compound using a 10 to 12 inch drywall knife.
Dust or residue may prevent the joint compound from sticking to the sheetrock.